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Date:   Thu, 21 May 2020 15:21:25 +0530
From:   Pavan Kondeti <pkondeti@codeaurora.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org,
        Vinayak Menon <vinmenon@codeaurora.org>,
        Ben Dooks <ben.dooks@codethink.co.uk>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Steven Rostedt (VMware)" <rostedt@goodmis.org>,
        Liang Chen <cl@rock-chips.com>
Subject: Re: [PATCH] kthread: Use TASK_IDLE state for newly created kernel
 threads
Message-ID: <20200521095125.GD31725@codeaurora.org>
References: <1589975710-9283-1-git-send-email-pkondeti@codeaurora.org>
 <20200520181858.GA343493@kroah.com>
 <20200521013544.GC31725@codeaurora.org>
 <20200521055639.GA2337399@kroah.com>
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On Thu, May 21, 2020 at 07:56:39AM +0200, Greg Kroah-Hartman wrote:
> On Thu, May 21, 2020 at 07:05:44AM +0530, Pavan Kondeti wrote:
> > On Wed, May 20, 2020 at 08:18:58PM +0200, Greg Kroah-Hartman wrote:
> > > On Wed, May 20, 2020 at 05:25:09PM +0530, Pavankumar Kondeti wrote:
> > > > When kernel threads are created for later use, they will be in
> > > > TASK_UNINTERRUPTIBLE state until they are woken up. This results
> > > > in increased loadavg and false hung task reports. To fix this,
> > > > use TASK_IDLE state instead of TASK_UNINTERRUPTIBLE when
> > > > a kernel thread schedules out for the first time.
> > > > 
> > > > Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
> > > > ---
> > > >  kernel/kthread.c | 6 +++---
> > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/kernel/kthread.c b/kernel/kthread.c
> > > > index bfbfa48..b74ed8e 100644
> > > > --- a/kernel/kthread.c
> > > > +++ b/kernel/kthread.c
> > > > @@ -250,7 +250,7 @@ static int kthread(void *_create)
> > > >  	current->vfork_done = &self->exited;
> > > >  
> > > >  	/* OK, tell user we're spawned, wait for stop or wakeup */
> > > > -	__set_current_state(TASK_UNINTERRUPTIBLE);
> > > > +	__set_current_state(TASK_IDLE);
> > > >  	create->result = current;
> > > >  	/*
> > > >  	 * Thread is going to call schedule(), do not preempt it,
> > > > @@ -428,7 +428,7 @@ static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
> > > >  
> > > >  void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
> > > >  {
> > > > -	__kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
> > > > +	__kthread_bind_mask(p, mask, TASK_IDLE);
> > > >  }
> > > >  
> > > >  /**
> > > > @@ -442,7 +442,7 @@ void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
> > > >   */
> > > >  void kthread_bind(struct task_struct *p, unsigned int cpu)
> > > >  {
> > > > -	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
> > > > +	__kthread_bind(p, cpu, TASK_IDLE);
> > > >  }
> > > >  EXPORT_SYMBOL(kthread_bind);
> > > 
> > > It's as if people never read mailing lists:
> > > 	https://lore.kernel.org/r/DM6PR11MB3531D3B164357B2DC476102DDFC90@DM6PR11MB3531.namprd11.prod.outlook.com
> > > 
> > > Given that this is an identical resend of the previous patch, why are
> > > you doing so, and what has changed since that original rejection?
> > > 
> > I did not know that it is attempted before. Thanks for pointing to the
> > previous discussion. 
> > 
> > We have seen hung task reports from customers and it is due to a downstream
> > change which create bunch of kernel threads for later use.
> 
> Do you have a pointer to that specific change?
> 
Here it is
https://source.codeaurora.org/quic/la/kernel/msm-4.19/commit/drivers/staging/android/ion/ion_system_heap.c?h=LA.UM.8.12.r1-11300-sm8250.0&id=0734b477f1e77cb9f91f5e5c0d7742d3113f2cd3

> > From Peter's reply, I understood that one must wake up the kthread
> > after creation and put it in INTERRUPTIBLE sleep. I will pass on the
> > message.
> 
> Just go fix that code, it sounds like it's in your tree already :)
> 
Yes, we will fix it.

Thanks,
Pavan
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